Phased arrays are well known in the fields of microwave and radio frequency detection and communication. In those fields, the typical phased array is a phase-coherent arrangement of antenna elements with electronic phase and amplitude control for each element, which is used to shape and direct the beam.
More recently, it has been recognized that phased arrays can also be used to steer optical, e.g. infrared, beams. In an approach based on diffraction of the beam by gratings, for example, wavelength tuning is used to steer the beam along one axis, and phase control is used to steer the beam along the orthogonal axis. Such an approach is described, for example, in the following publications: K. Van Acoleyen, H. Rogier, and R. Baets, “Two-dimensional optical phased array antenna on silicon-on-insulator,” Opt. Express 18(13), 13655-13660 (2010); and J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, L. A. Coldren, and J. E. Bowers, “Two-dimensional free-space beam steering with an optical phased array on silicon-on-insulator,” Opt. Express 19(22), 21595-21604 (2011). Further, the use of thermo-optical tuning in a phased array of dielectric grating elements is described, e.g., in J. Sun, E. Timurdogan, A. Yaacobi, E. Shah Hosseini, D. Coolbaugh, and M. R. Watts, “Large-scale nanophotonic phased array,” Nature (London), 493, 195-199 (2013).
Although such approaches are useful, there remains a need for additional approaches to optical beam steering, particularly if such approaches can provide both a wide frequency-tuning range and a wide two-dimensional scan range in a chip-scale device.